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SSH

Add public key to server from Github 

mkdir -p -m 700 ~/.ssh; echo "$(curl -s https://github.com/aikedejongste.keys) # Aike" >> ~/.ssh/authorized_keys; chmod 600 ~/.ssh/authorized_keys

Use SSH to proxy SSH to other machine with config

Put this in .ssh/config

Host alias-name-you-ssh-to     # use with "ssh alias-name-you-ssh-to"
  Hostname 10.10.10.10         # actual IP of destination host
  ProxyJump real.hostname.com  # actual hostname of the server you want to jump through
  User aike                    # optional username on jump host
  Port 2222                    # optional port on jump host

Use SSH to proxy SSH to other machine cli 

ssh -A -W '[10.10.10.10]:22' real.hostname

Try ssh until it is ready 

until ssh 10.10.1.3; do sleep 1; done

or

ssh -o 'ConnectionAttempts 999' 10.10.1.3

Generate key 

ssh-keygen -o -a 100 -t ed25519 -f ~/.ssh/id_ed25519 -C "john@example.com"

AutoSSH

Make a firewall host reachable over reverse SSH tunnel with AutoSSH:

autossh -nNT -R 2222:localhost:22 user@remote.box

so you can ssh to remote.box:2222.

Ansible add ssh fingerprint to known hosts 

- name: update known hosts file
  shell: ssh-keyscan -H "" >> ~/.ssh/known_hosts
  loop:
    - 10.10.1.2

Enable root login with password (bad idea) 

sudo sed -i 's/PasswordAuthentication no/PasswordAuthentication yes/' /etc/ssh/sshd_config
sudo sed -i 's/PermitRootLogin prohibit-password/PermitRootLogin yes/' /etc/ssh/sshd_config
sudo systemctl restart sshd

Check forwarded and available keys 

ssh-add -l